The invention concerns a filter element for filtering a liquid medium, in particular motor oil or transmission oil. The filter element comprises a first end plate and a second end plate as well as a filter material or filter medium that is arranged between the two end plates and that can be flowed through by the liquid medium to be filtered in a flow direction that is radial to the longitudinal axis of the filter element. In the flow direction downstream of the filter element, a clean chamber of the filter element is arranged that is fluidically connected with a liquid medium outlet of the filter element. The filter element is provided with a so-called bypass duct or circumventing duct for the liquid medium by means of which the liquid medium, by bypassing the filter material, can be guided through the filter element. The bypass duct is fluidically connected by means of a bypass valve with the clean chamber and has an inlet for the liquid medium embodied by the first end plate. The bypass duct has a sieve associated therewith in order to separate solid materials from the liquid medium that is guided through the bypass duct. The invention concerns moreover a filter assembly with such a filter element.
It is known to employ filter elements in motor vehicles in which the medium to be filtered, not least for avoiding overpressure-caused damage of the filter material, is guided by means of the bypass duct past the filter material. This is, for example, necessary in case of oil filters when the liquid medium, i.e., for example, transmission oil or motor oil, is not yet liquid enough upon cold start of the motor vehicle, i.e., still has a viscosity that is too high in order to pass through the filter material. By means of this bypass a satisfactorily high medium flow via the filter element can be ensured in any case.
U.S. 2010/0126920 A1 discloses the provision of an overflow for embodying a bypass of the filter material. U.S. 2002/0074272 A1 proposes on the other hand to provide a pressure relief valve for bypassing a filter material.
Bypassing the filter material entails in principle the risk that the liquid medium after exiting from the filter element still contains larger dirt particles. U.S. 2004/0164008 A1 proposes therefore to arrange at a bypass valve a coarse- mesh sieve in order to filter out at least the coarser and coarse dirt particles from the medium to be filtered.
The arrangement of a sieve for coarse filtration of the medium to be filtered is also known from DE 10 2010 054 349 A1 and WO 2012/110411 A1. The known sieves are arranged in this context fluidically downstream of the bypass valve so that the bypass valve may be contaminated with dirt particles. This may lead to functional impairment of the bypass valve.
DE 200 06 972 U1 and DE 200 06 974 U1 disclose in contrast thereto the arrangement of a sieve fluidically upstream of the bypass valve. The sieve is arranged in a cover element that is clipped on seal-tightly from the exterior onto the end plate, provided with the inlet of the bypass duct, of the filter element. Accordingly, the bypass valve can be protected indeed from the negative effects of the coarse solid material contaminants in the liquid medium. However, at the same time the constructive height of the filter element is increased. Moreover, the required pressure-tight and fluid-tight sealing action of the sieve or of the cover element relative to the filter element is complex, expensive, and failure-prone.